Elevation estimates have changed

In may and june I created some routes through the French Alps, and noted all total elevation estimates down. When I now open the same routes, the estimates are quite different; all much lower: a route that was supposed to climb a total of 3000 meters, now shows 1800; 3200 has become 1700; 3300 - 2200; 3500 - 1800; 3800 - 2100, etcetera. The same applies to routes in the Swiss Alps and the Vosges mountains, although the differences there are somewhat smaller. This sudden change seems to have occurred in september. What happened?